1. Technical Field of the Invention
The present invention relates to optical recording media such as a disc-shaped optical disk and rectangular optical card in which an information signal can additionally be recorded by heat of a laser beam only once, and a recording method onto the optical recording medium.
2. Description of the Related Art
Optical recording media such as a disc-shaped optical disk and rectangular optical card have been frequently used, because various information such as video information, sound information, and computer data can be recorded in large capacities and desired information can be accessed at a high speed.
This type of optical recording medium can roughly be classified into a ROM type and an additionally recordable type.
For the above-described optical recording medium of the ROM type, an injection molder is used to convert an information signal to be recorded into a pit string including a plurality of pits on a transparent resin substrate, and a reflective film and protective film are successively formed on a surface in which the pit string is carved, for example, as a spiral track to form the medium. Moreover, a transparent resin substrate side is irradiated with a laser beam for reproduction from an optical pickup disposed so as to be movable in an optical recording medium drive, and the information signal is reproduced with a return light of the laser beam from the reflective film by the pit string.
On the other hand, for the optical recording medium of the additionally recordable type, the injection molder is used to form, for example, a groove having a predetermined depth, which is a recording track, in a spiral shape in the transparent resin substrate, and a recording film, reflective film, and protective film are successively formed on the surface including the groove. Moreover, the transparent resin substrate side is irradiated with the laser beam for recording from the optical pickup disposed so as to be movable in the optical recording medium drive, and the information signal to be recorded is recorded in the groove on the recording film. After the recording, in the same manner as in the ROM type, the transparent resin substrate side is irradiated with the laser beam for reproduction, and the information signal is reproduced with the return light of the laser beam from the reflective film by a light reflectance change.
Additionally, the optical recording medium of the ROM type can inexpensively be obtained by mass production. However, from a manufacturing aspect, it is difficult to record information which differs with each medium, such as unique ID information, on the medium of the ROM type. In a more concrete example, with respect to information (software) recorded in a compact disc-read only memory (CD-ROM) which is well known as the ROM type, there has been a demand for the recording of individual information such as ID information for each CD-ROM.
When there is such demand, the following “first to third methods” can be applied.
[First Method]
A first method comprises: using the optical recording media of the additionally recordable type which can inexpensively be obtained, such as a compact disc-recordable (CD-R) in which the information signal can be written only once, and a compact disc-rewritable (CD-RW) in which the signal can be written a plurality of times, to record the unique ID information in each medium.
FIGS. 1A to 1C are an appearance perspective view, partial enlarged plan view, and longitudinal sectional view showing a well-known CD-R which is the optical recording medium of the additionally recordable type.
As shown in FIGS. 1A to 1C, in a conventional CD-R 100, transparent resin materials such as polycarbonate are used to mold a disc-shaped transparent resin substrate 101 which has an outer diameter of 120 mm, center hole diameter of 15 mm, and thickness of 1.2 mm. In this case, on one surface 101a side, a wobbled groove 102 is formed beforehand in a spiral shape toward an outer periphery from an inner periphery with substantially predetermined depth and pitch, and a land 103 is formed beforehand between the grooves 102, 102 formed adjacent to each other.
In this case, the groove 102 is wobbled as a guide track for additionally recording the information in a sinusoidal wave form on left and right sides of the groove by a wobble signal which has a center frequency of about 22 KHz. Moreover, an absolute time in pregroove (ATIP) signal is superimposed as recording position information indicating a recording position of the information signal upon the wobble signal, and thereby the recording position information is recorded beforehand in the groove 102. Concretely, FM modulation is applied about ±1 KHz centering on the wobble signal center frequency of about 22 KHz to superimpose the ATIP signal.
Furthermore, after the groove 102 and land 103 are formed on one surface 101a of the transparent resin substrate 101, the groove 102 and land 103 are coated with a recording film 104 of an organic dyestuff in a spin coat method. A metal reflective film 105 of aluminum, silver, or gold, and a protective film 106 of an ultraviolet curing resin are successively formed on the recording film 104.
When the CD-R 100 including the recording film 104 as described above is used, the wobbled groove 102 is irradiated with the laser beam for the recording from the optical pickup disposed so as to be movable in a CD-R drive (not shown) on a side of another surface 101b of the transparent resin substrate 101. The ATIP signal is extracted from the wobble signal by the groove 102, and the information to be recorded, which is converted into an EFM signal, is recorded as a reflectance change at a heat melting time of the organic dyestuff by the laser beam at a recording position on the groove 102 according to the ATIP signal. Therefore, the information signal can additionally be recorded only once in the groove 102 on the recording film 104. In this case, by only one additional recording, important ID information unique to the medium, which must not be permitted to be rewritten by alternation, can be recorded. However, for example, the recording of a large number of CD-R 100 exceeding 100 thousand discs by the CD-R drive raises a problem in a recording time and recording apparatus.
[Second Method]
A second method comprises: using a technical idea of optical recording medium disclosed in Japanese Patent Application Laid-Open No.8-124219 to irradiate the optical recording medium of the ROM type with an intense laser beam and to partially deform the transparent resin substrate so that the individual identification information is additionally recorded.
FIG. 2 is a longitudinal sectional view showing the optical recording medium of the ROM type as a related art in which the transparent resin substrate is irradiated with the intense laser beam and can partially be deformed.
As shown in FIG. 2, in an optical recording medium (CD-ROM) 200 of the ROM type, a plurality of pits 202 are carved in concave shapes on a transparent resin substrate 201 by injection molding by a stamper. A metal reflective film 203 of aluminum or gold, and a protective film 204 by the UV curable resin are successively formed on the pits 202.
Moreover, after the transparent resin substrate 201 is injection-molded, the metal reflective film 203 is irradiated with the intense laser beam of about 20 mW/μm2. Then, the pits 202 are deformed like pits 205 by heat energy absorbed by the metal reflective film 203 to form rims 206 around the pits 205, and thereby mixed presence of the non-deformed pits 202 and deformed pits 205 can realize additional recording of individual key information.
Furthermore, as omitted from the drawing, there is also disclosed a method comprising: collapsing a part of the pit string of the pits 202 by the heat of the intense laser beam; and additionally recording the individual key information on the collapsed portions.
Additionally, as omitted from the drawing, there is also disclosed a method comprising: disposing a portion of about 1 mm in which the pits 202 are not formed in a part of the pit string constituting the track; irradiating the portion with the intense laser beam; and thermally deforming the transparent resin substrate 201 with the heat energy to additionally record the individual key information.
However, the injection-molded optical recording medium 200 has eccentricity and surface deflection. Therefore, unless recording position information obtained from recorded pit information is servo-laser recorded, it is impossible to physically deform the specified portion on the transparent resin substrate 201. In the above-described publication, a method of specifying the specified portion in additionally recording the individual key information on the transparent resin substrate 201, and a method of performing the servo additional recording are not disclosed.
[Third Method]
A third method comprises: using the technical idea of an optical disk disclosed in Japanese Patent Application Laid-Open No.7-93810 to irradiate the optical disk of the additionally recordable type with the intense laser beam and to make a hole in the reflective film.
FIG. 3 is a longitudinal sectional view showing the optical disk of the additionally recordable type as a related art which can be irradiated with the intense laser beam to make the hole in the reflective film.
As shown in FIG. 3, in an optical disk 300 of the additionally recordable type, on a substrate 301 formed of glass or plastic, an amorphous thin film 302 of As—S—Te or Ge—Sb—Te, a metal thin film 303 of Ag or Al, a buffer film 304 of SiO or ZnS, a reflective film 305 of Ag, and a protective film 306 of plastic are successively formed.
Moreover, when a substrate 301 side is irradiated with an irradiation light amount P1, temperature of the amorphous thin film 302 rises at T1° C., but the metal is not rapidly diffused in the amorphous thin film 302. It is also disclosed that the reflectance seen from the substrate 301 side does not change.
Furthermore, it is disclosed that the substrate 301 side is irradiated with an irradiation light amount P2, then the temperature of the amorphous thin film 302 rises at T2° C., the metal is rapidly diffused in the amorphous thin film 302, therefore the reflectance of a portion with the metal diffused therein becomes lower than that of an original laminated film, and transmittance increases to about 90%.
Additionally, it is disclosed that the substrate 301 side is irradiated with an irradiation light amount P3, then the temperature of the amorphous thin film 302 rises at T3° C., the amorphous thin film 302, metal thin film 303, buffer film 304, and reflective film 305 are molten, each film is pulled toward the periphery by surface tension to thereby make a hole in each film, and the reflectance seen from the substrate 301 side decreases to about 5%.
In the related art of the above-described publication, in the media in which the information can be rewritten, a method is disclosed comprising: changing the reflectance of the reflective film 305 at pit and non-pit portions in order to prevent once recorded data from being deleted or altered.
However, in the related art, a recording method onto a non-recorded portion in which there is not any pit is not disclosed.